American Crossroads, the biggest of the Republican "super PACs," is planning to begin its first major anti-Obama advertising blitz of the year, a moment the Obama re-election campaign has been girding for and another sign that the general election is starting in earnest.

With an anticipated bank account of more than $200 million, officials at American Crossroads said they would probably begin their campaign this month. But they said they would focus the bulk of the first phase from May through July, which they believe is a critical period for making an impression on voters, before summer vacations and the party conventions take place.

Steven J. Law, the group's leader, said the ads would address the challenge of unseating a president who polls show is viewed favorably even though many people disapprove of his handling of the economy. Basically, Mr. Law said, "how to dislodge voters from him."

The ultimate goal of the Crossroads campaign, Mr. Law said, would be to better connect Americans' disappointment with the economy to their views of the president, especially among crucial swing voters.

The Crossroads advertising push — the timing of which has been the subject of avid speculation at the Obama campaign headquarters in Chicago — would give the campaign of Mitt Romney, the Republican front-runner, the time and cover to map out its national organization, replenish its bank account and put the finishing touches on its own long-discussed advertising plan, which is expected to highlight the economic pain of ordinary Americans.

Crossroads was founded with help from the Republican strategists Karl Rove and Ed Gillespie — the latter just signed on as an adviser to Mr. Romney — and so far it has largely been sitting on the sidelines, studying the electorate and planning for the fall as the Republican nominating contest continued.

Its decision to enter now is helped by a growing perception that the Republican race is nearly over and that Mr. Romney is the presumed nominee, particularly as speculation increases about the future of the candidacy of Rick Santorum (who is not campaigning for several days because of his daughter Bella's illness). And Crossroads' planned intervention affirms predictions that the general election campaign will be fought in large part by proxy, via the super PACs, which have been emboldened by the Supreme Court's Citizens United ruling in 2010 that helped pave the way for their creation.

Combined with expected activity from a pro-Romney super PAC, Restore Our Future, and a Republican National Committee with better finances than expected, Crossroads is helping to ease fears among some Republicans that Mr. Obama's projected financial advantage — with more than $80 million on hand and expectations to have raised at least $750 million all told — would overwhelm Mr. Romney, who had $7.3 million on hand in his last filing report from February, especially at the start.

The prolonged and hard-fought nominating contest, Mr. Romney's advisers said, has put his campaign nearly two months behind on its initial plan to build political and field operations in the dozen states where both sides agree that most of the general election will be fought: Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin. (In the final phase of the campaign, Romney officials believe that the election could come down to just four states: Colorado, Nevada, Ohio and Virginia.)

Republican elected officials and strategists acknowledged in interviews that Mr. Romney had significant ground to make up — Mr. Obama leads in many early polls of swing states.

Gov. John R. Kasich, Republican of Ohio, where Mr. Romney narrowly beat Mr. Santorum, said Mr. Romney needed to show that he can connect with voters and "demonstrate that he understands their problems." But, Mr. Kasich added, "There is going to be a part of the electorate that is a lot more interested in beating Obama than electing the Republican."

The Republican primary season, which veered into fights over contraception, abortion and immigration, has lifted the gloom Democrats had been feeling.

Gov. Jerry Brown of California said he became more optimistic about Mr. Obama's re-election chances after "the Republican primaries gave us these dramatic performances" that pushed Mr. Romney "farther and farther from the center of gravity in American politics."

Obama campaign aides said they would not give Mr. Romney any room to recover from what several polls show to be high unfavorable ratings. A new fusillade of commercials, Web videos and Twitter posts is painting Mr. Romney as a disconnected businessman who favors the rich and will keep in place the approach that caused the financial crisis and put an unfair burden on the middle class and the poor.

David Axelrod, a senior Obama strategist, made a similar argument against American Crossroads on Sunday when asked to address its planned campaign against the president. "That's going to be a tough sell," he said, adding that voters "would see right through those who want to go back to the same failed policies that were so punishing for them and the entire country."

Mr. Obama has his own supportive super PAC, Priorities USA Action, which is now sifting through Mr. Romney's most embarrassing campaign moments for its expected volley of commercials.

But Priorities USA Action is not nearly as well-financed as its Republican rivals. The group and its issues-oriented partner, Priorities USA, raised $6.1 million last year, with donations from the film executive Jeffrey Katzenberg, the Service Employees International Union and the United Auto Workers union.

American Crossroads and its affiliated Crossroads GPS raised $51 million last year, according to federal election filings, much of it from the conservative financier Harold C. Simmons and other wealthy donors with interests in coal, real estate and finance.

These groups will be formidable allies for Mr. Romney's campaign. Though they are legally prohibited from coordinating with his strategists, they are working on the same mission, to shift the debate away from issues of wealth inequality — terrain that appears to favor Mr. Obama — and toward what Stuart Stevens, a senior Romney strategist, said would be a referendum on the president and his promise to of economic recovery.

"There's a sense of anxiety out there that's tremendous," Mr. Stevens said. "It's home heating costs, it's gas prices, the price of food is up. What about people's everyday lives is easier today than it was four years ago?"

But, Mr. Law said, Crossroads research suggests that Mr. Obama's campaign has started to gain traction among critical swing voters by arguing that Republicans, including Mr. Romney, favor an "economic plutocracy" in which middle-class voters can no longer count on financial security, even though they work hard and play by the rules.

"His argument is: 'The reason you feel bad is not because I've been an inadequate president but because the rules of the game are stacked against you,' " Mr. Law said. Calling it a "dystopian vision," he added, "that narrative has some gravitational pull."

But, Mr. Law said, interviews with independent voters, as well as uncommitted Democrats and Republicans who supported Mr. Obama in 2008, have revealed an alternate "emerging view" that Crossroads will seek to solidify, "that Obama just may not be up to the job, he can't seem to fix things he promised he would fix."

Though Mr. Law would not discuss the planned Crossroads ads in detail, he indicated that the first ones would try not to offend the sensibilities of swing voters who still like Mr. Obama, apparently in part for fear of rallying them to his side.

For all of that, both sides agree that the outcome could depend on events largely out of their control, most of them linked to the economy.

"The biggest issue," said Gov. Rick Scott, Republican of Florida, "is still jobs."

Prior to joining The New York Times in September 2006, he was a national political correspondent for the Chicago Tribune.

Mr. Zeleny joined the Chicago Tribune in 2000 as a reporter on the Metropolitan desk in Chicago, where he was a member of the reporting team that won a Pulitzer Prize in explanatory journalism for documenting gridlock in the nation's air traffic system.

American Crossroads, the biggest of the Republican "super PACs," is planning to begin its first major anti-Obama advertising blitz of the year, a moment the Obama re-election campaign has been girding for and another sign that the general election is starting in earnest.

With an anticipated bank account of more than $200 million, officials at American Crossroads said they would probably begin their campaign this month. But they said they would focus the bulk of the first phase from May through July, which they believe is a critical period for making an impression on voters, before summer vacations and the party conventions take place.

Steven J. Law, the group's leader, said the ads would address the challenge of unseating a president who polls show is viewed favorably even though many people disapprove of his handling of the economy. Basically, Mr. Law said, "how to dislodge voters from him."

The ultimate goal of the Crossroads campaign, Mr. Law said, would be to better connect Americans' disappointment with the economy to their views of the president, especially among crucial swing voters.

The Crossroads advertising push — the timing of which has been the subject of avid speculation at the Obama campaign headquarters in Chicago — would give the campaign of Mitt Romney, the Republican front-runner, the time and cover to map out its national organization, replenish its bank account and put the finishing touches on its own long-discussed advertising plan, which is expected to highlight the economic pain of ordinary Americans.

Crossroads was founded with help from the Republican strategists Karl Rove and Ed Gillespie — the latter just signed on as an adviser to Mr. Romney — and so far it has largely been sitting on the sidelines, studying the electorate and planning for the fall as the Republican nominating contest continued.

Its decision to enter now is helped by a growing perception that the Republican race is nearly over and that Mr. Romney is the presumed nominee, particularly as speculation increases about the future of the candidacy of Rick Santorum (who is not campaigning for several days because of his daughter Bella's illness). And Crossroads' planned intervention affirms predictions that the general election campaign will be fought in large part by proxy, via the super PACs, which have been emboldened by the Supreme Court's Citizens United ruling in 2010 that helped pave the way for their creation.

Combined with expected activity from a pro-Romney super PAC, Restore Our Future, and a Republican National Committee with better finances than expected, Crossroads is helping to ease fears among some Republicans that Mr. Obama's projected financial advantage — with more than $80 million on hand and expectations to have raised at least $750 million all told — would overwhelm Mr. Romney, who had $7.3 million on hand in his last filing report from February, especially at the start.

The prolonged and hard-fought nominating contest, Mr. Romney's advisers said, has put his campaign nearly two months behind on its initial plan to build political and field operations in the dozen states where both sides agree that most of the general election will be fought: Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin. (In the final phase of the campaign, Romney officials believe that the election could come down to just four states: Colorado, Nevada, Ohio and Virginia.)

Republican elected officials and strategists acknowledged in interviews that Mr. Romney had significant ground to make up — Mr. Obama leads in many early polls of swing states.

Gov. John R. Kasich, Republican of Ohio, where Mr. Romney narrowly beat Mr. Santorum, said Mr. Romney needed to show that he can connect with voters and "demonstrate that he understands their problems." But, Mr. Kasich added, "There is going to be a part of the electorate that is a lot more interested in beating Obama than electing the Republican."

The Republican primary season, which veered into fights over contraception, abortion and immigration, has lifted the gloom Democrats had been feeling.

Gov. Jerry Brown of California said he became more optimistic about Mr. Obama's re-election chances after "the Republican primaries gave us these dramatic performances" that pushed Mr. Romney "farther and farther from the center of gravity in American politics."

Obama campaign aides said they would not give Mr. Romney any room to recover from what several polls show to be high unfavorable ratings. A new fusillade of commercials, Web videos and Twitter posts is painting Mr. Romney as a disconnected businessman who favors the rich and will keep in place the approach that caused the financial crisis and put an unfair burden on the middle class and the poor.

David Axelrod, a senior Obama strategist, made a similar argument against American Crossroads on Sunday when asked to address its planned campaign against the president. "That's going to be a tough sell," he said, adding that voters "would see right through those who want to go back to the same failed policies that were so punishing for them and the entire country."

Mr. Obama has his own supportive super PAC, Priorities USA Action, which is now sifting through Mr. Romney's most embarrassing campaign moments for its expected volley of commercials.

But Priorities USA Action is not nearly as well-financed as its Republican rivals. The group and its issues-oriented partner, Priorities USA, raised $6.1 million last year, with donations from the film executive Jeffrey Katzenberg, the Service Employees International Union and the United Auto Workers union.

American Crossroads and its affiliated Crossroads GPS raised $51 million last year, according to federal election filings, much of it from the conservative financier Harold C. Simmons and other wealthy donors with interests in coal, real estate and finance.

These groups will be formidable allies for Mr. Romney's campaign. Though they are legally prohibited from coordinating with his strategists, they are working on the same mission, to shift the debate away from issues of wealth inequality — terrain that appears to favor Mr. Obama — and toward what Stuart Stevens, a senior Romney strategist, said would be a referendum on the president and his promise to of economic recovery.

"There's a sense of anxiety out there that's tremendous," Mr. Stevens said. "It's home heating costs, it's gas prices, the price of food is up. What about people's everyday lives is easier today than it was four years ago?"

But, Mr. Law said, Crossroads research suggests that Mr. Obama's campaign has started to gain traction among critical swing voters by arguing that Republicans, including Mr. Romney, favor an "economic plutocracy" in which middle-class voters can no longer count on financial security, even though they work hard and play by the rules.

"His argument is: 'The reason you feel bad is not because I've been an inadequate president but because the rules of the game are stacked against you,' " Mr. Law said. Calling it a "dystopian vision," he added, "that narrative has some gravitational pull."

But, Mr. Law said, interviews with independent voters, as well as uncommitted Democrats and Republicans who supported Mr. Obama in 2008, have revealed an alternate "emerging view" that Crossroads will seek to solidify, "that Obama just may not be up to the job, he can't seem to fix things he promised he would fix."

Though Mr. Law would not discuss the planned Crossroads ads in detail, he indicated that the first ones would try not to offend the sensibilities of swing voters who still like Mr. Obama, apparently in part for fear of rallying them to his side.

For all of that, both sides agree that the outcome could depend on events largely out of their control, most of them linked to the economy.

"The biggest issue," said Gov. Rick Scott, Republican of Florida, "is still jobs."

Prior to joining The New York Times in September 2006, he was a national political correspondent for the Chicago Tribune.

Mr. Zeleny joined the Chicago Tribune in 2000 as a reporter on the Metropolitan desk in Chicago, where he was a member of the reporting team that won a Pulitzer Prize in explanatory journalism for documenting gridlock in the nation's air traffic system.